Mold resistant exterior wall assembly

ABSTRACT

A mold resistant exterior wall assembly incorporating a steel stud frame with an interior gypsum wall product attached to the interior of the frame and a mold resistant exterior gypsum wall product attached to the exterior of the frame forming a cavity therebetween. The joints of the exterior gypsum wall product are taped and the entire surface of the exterior gypsum wall product is coated with a liquid applied elastomeric (greater than 25% elongation) air/water barrier and vapor retarder/barrier. Once the elastomeric liquid is applied and set, rigid foam plastic insulation is applied. Exterior veneer is applied a predetermined distance from the rigid foam plastic insulation.

This application claims priority to U.S. Provisional Application Ser. No. 60/563,226 filed Apr. 19, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Applicant's invention relates to an exterior wall assembly for use in residential and commercial construction. More specifically, the present invention relates to a mold, mildew and fungus resistant insulated steel stud frame exterior wall assembly.

2. Background Information

Nowadays, the public has become increasing aware of the indoor air quality dangers posed by mold, mildew and fungus. Too much mold, mildew, or fungus can affect health and damage or destroy building materials. Molds, mildew, and fungus are decomposers of dead organic material, such as leaves and wood. Since mold, mildew, and fungus decompose dead organic matter, they can also grow on paper facing on gypsum board (drywall) and other materials made from wood. Mold, mildew, and fungus can also digest some synthetic materials such as adhesives, pastes and paints. While mold, mildew, and fungus cannot get nutrients from inorganic material such as concrete, glass and metal, they can grow on the dirt present on these surfaces. Mold, mildew, and fungus need water to grow in addition to food, oxygen and a temperature between 40 degrees and 100 degrees Fahrenheit. Mold, mildew and fungus prefer damp or wet material and some can get moisture from the air when the air is very damp (greater than 70% humidity). Mold, mildew and fungus can also make spores which can be released and carried by air or water to new locations. When mold, mildew, or fungus spores land on a damp surface that has food and oxygen available, and if the temperature is appropriate, they will start to grow. Mold, mildew, and fungus spores are present in both indoor and outdoor air.

The use of steel studs in construction can facilitate mold, mildew, and fungus growth in interior walls. Building a structure with steel studs is generally less energy efficient than building with wood because metal transfers heat and cold much more readily than wood. Essentially steel studs can create thermal bridges to the outside of a structure causing rapid changes in the temperature of the steel studs leading to water condensation along the studs.

A primary goal in steel stud construction is to prevent the growth and accumulation of mold, mildew, and fungus in the vicinity of the steel studs and thus indoors that would otherwise lead to occupant health problems and potentially damage or destroy building materials. The present inventor found that a significant number of mold, mildew, and fungus problems are due to the use of inappropriate building materials or the treatment of a single building component as a complete system in steel stud construction. In traditional steel stud frame construction, an interior wall gypsum product is attached to the interior surface of a steel stud frame and an exterior wall gypsum product is attached to the exterior of the steel stud frame. The cavity formed between the interior wall gypsum product and the exterior wall gypsum product is filled with fiberglass batt insulation. The exterior gypsum board is generally covered with either 15# tar paper or a non-elastic (less than 1% elongation) asphalt based dampproofing material. Exterior veneer, such as brick, stucco, or steel siding is assembled a predetermined distance from the tar paper or dampproofing material. This assembly allows the dew point (condensation point) to be reached within the cavity either on the face of the interior wall gypsum product or on the fiberglass batt insulation causing mold and mildew growth that can breach the interior of the bulding leading to allergic reactions and a decline in the indoor air quality (IAQ).

No one has yet developed a wall system that will solve these mold, mildew, and fungus problems that are associated with steel stud construction. In order to prevent the growth of mold, mildew, and fungus, moisture, air leakage, and food source for the mold, mildew, and fungus must be eliminated.

The building products that provide the least food value and most moisture resistance are American Society for Testing and Materials (ASTM) standard C 1177 moisture resistant gypsum board and ASTM C 578 Type IV & X Extruded Polystyrene. ASTM C 1177 products include DensGlass Gold® and DensShield® by Georgia-Pacific. Examples of ASTM C 578 products include Foamular® by Owens Corning and Styrofoam™ by Dow. Dow Styrofoam™ products include Square Edge™, Score Board™, and CavityMate™. Another foam plastic product by Dow is Dow Quik R™.

In order to eliminate air leakage and ultimately mold, mildew, and fungus growth, the present inventor has determined an air barrier must be used. An air barrier is also useful for waterproofing concrete masonry unit (CMU) walls. These products are either brush or spray applied and are highly elastomeric. The preferred products for the present invention are spray applied polymer modified asphalt liquid. A spray applied air barrier is preferred by the present inventor because it is seamless, can accommodate any building movement, and generally lowers the air leakage rate to 0.0004 cubic feet per minute per square foot (cfm/ft²), resistance to gust winds for 62.8 pounds per square foot (lbs/ft²) and sustained winds for 20.9 pounds per square foot (lbs/ft²) with no delamination or increase in air leakage rates. Air barriers are to be distinguished from air infiltration barriers. Air infiltration barriers are not air or water leakage barriers, but do enhance cavity wall performance by retarding air flow.

Steel studs are commonly used in construction, but provide a haven for mold, mildew, and fungus growth. Steel stud construction with R-11 batt insulation is not an R-11 wall. The R-11 batt insulation is placed between the steel studs leaving the studs uninsulated. Due to thermal leakage of the steel studs, the R-value for the wall is only approximately R-7.7 to R-7.9. Condensation begins at the uninsulated steel studs. This condensation will permit mold, mildew, and fungus growth. The present inventor has found that removing the batt insulation from between the steel studs and using moisture and mold resistant gypsum board on one or both sides of the steel studs can prevent mold, mildew, and fungus growth in the vicinity of the steel studs. To obtain a truly R-11 wall along with the moisture and mold resistance the present inventor has found that utilizing extruded polystyrene insulation (XEPS) around the steel studs will decrease the thermal leakage from the studs without providing a food source to mold, mildew or fungus. In addition, raising the R-value of the wall assembly to 13.9 will help to achieve the appropriate R-11 value.

The present mold resistant exterior wall assembly was designed with these specifications in mind ultimately combining air and water barriers, vapor retarders, and mold resistant components while moving the dew point (condensation point) away from the steel studs.

More particularly, the preferred embodiment of the present invention does not utilize fiberglass batt insulation which acts as a nest for mold growth. Instead, the cavity between the interior wall gypsum product and the exterior wall gypsum product in the preferred embodiment is left empty. The exterior gypsum wall product is mold resistant preferably meeting ASTM C 1177. Once the exterior gypsum wall product is in place, its joints are taped and the entire surface of the exterior gypsum wall product is coated with a liquid applied elastomeric (greater than 25% elongation) air/water barrier and vapor retarder which prevents liquid water and humidity from passing into the building. This is critical as water or humidity greater than 70% is required for mold growth. Traditional tar paper and asphalt based dampproofing do not perform this function nor are they elastic enough (less than 1% elongation) to accommodate building movement. With building movement, these traditional products generally split apart permitting more water and/or humidity into the building interior which accomodates mold growth. Once the elastomeric liquid is applied and set, rigid foam plastic insulation (meeting the Montreal Protocol for CFCs for building codes and International Building Code/International Energy Conservation Code 2003 for energy conservation) is applied. This rigid foam plastic insulation moves the dew point (condensation point) away from the steel studs and the wall cavity.

Other benefits of this wall assembly include superior thermal efficiency as recognized by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 90.1. This is due to the use of the liquid applied air/water barrier which greatly reduces air infiltration into the building and by the application of the continuous rigid foam plastic insulation to the exterior of the steel studs. Thermal efficiency has increased from 50% to 80%.

In addition, the present invention utilizes sustainable/recyclable products that meet Environmental Protection Agency Volatile Organic Compound (EPA VOC) guidelines, the Montreal Protocol for CFC Reduction, and all known Code requirements while eliminating mold growth on the interior space of a building to improve indoor air quality.

SUMMARY OF THE INVENTION

The preferred embodiment of the present invention includes a mold resistant exterior wall assembly incorporating a steel stud frame with an interior gypsum wall product attached to the interior of the frame and a mold resistant exterior gypsum wall product attached to the exterior of the frame. Once both gypsum products are attached a cavity is formed therebetween. The joints of the exterior gypsum wall product are taped and the entire surface of the exterior gypsum wall product is coated with a liquid applied elastomeric air/water barrier and vapor retarder. Once the elastomeric liquid is applied and set, rigid foam plastic insulation is applied. Brick or steel siding veneer is applied a predetermined distance from the rigid foam plastic insulation.

The second embodiment of the present invention includes a mold resistant exterior wall assembly incorporating a steel stud frame with an interior gypsum wall product attached to the interior of the frame and a mold resistant exterior gypsum wall product attached to the exterior of the frame. Once both gypsum products are attached to the steel stud frame a cavity is formed therebetween. Fiberglass insulation is inserted within the cavity. The joints of the exterior gypsum wall product are taped and the entire surface of the exterior gypsum wall product is coated with a liquid applied elastomeric air/water barrier and vapor retarder. Once the elastomeric liquid is applied and set, rigid foam plastic insulation is applied. Metal lath is next applied followed by stucco.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the preferred embodiment of the present invention.

FIG. 2 is a perspective view of a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a perspective view of the preferred embodiment of the present invention is shown. More particularly, this preferred embodiment shows a mold resistant steel stud masonry veneer wall system 100. A foundation 102 is provided upon which the wall system 100 is assembled. The foundation 102 can consist of a crawlspace construction or slab-on-grade. A crawlspace foundation is a shallow and uninhabitable area between the soil and the first floor of the building. A crawlspace usually extends below the frost line or to a stable substrate. Crawlspaces are generally constructed with foundation walls and footings, however, piers may be used when the crawlspace is above grade. A slab-on-grade foundation is a concrete slab that is poured directly at ground level and acts as the first floor sub-surface. The slab is usually supported by continuous footing, piers or piles and grade beams.

Once the foundation 102 is in place, steel studs 106 are attached to the foundation 102. A plurality of these steel studs 106 acts as a frame for the wall system 100. The steel studs 106 depicted in FIG. 1 are more particularly C-shaped framing members typically used for axial load-bearing walls, curtain-walls, tall interior partitions, floorjoists, and roof truss assemblies. However, any appropriate steel studs may be used. Once the steel studs 106 are inserted a defined interior side 106 a and exterior side 106 b is established. The wall system 100 is constructed around the steel studs 106. Beginning at the interior side 106 a of the steel studs 106 is interior finish gypsum board 104. This interior finish gypsum board 104 is attached to the steel studs 106. A product that resists the development and spread of indoor contaminants, such as mold, mildew, and fungus, is preferred such as Dens Armor Plus™ by Georgia-Pacific. On the exterior side 106 b of the steel studs 106 is attached exterior gypsum board 108.

The exterior gypsum board 108 is preferably a glass mat gypsum substrate which is mold and moisture resistant. The glass mat gypsum substrate preferably contains a noncombustible water-resistant core, essentially gypsum, surfaced with a glass mat partially or completely embedded in the core. The water resistance of the glass mat gypsum substrate preferably has an average water absorption of not more than 10 weight percent after a two hour immersion. For code compliance purposes, the exterior gypsum board 108 should comply with the current ASTM standard C 1177. The thickness of the steel studs 106 provides an air space between interior finish gypsum board 104 and exterior gypsum board 108. The product Dens-Glass Gold™ by Georgia-Pacific possesses these preferred characteristics. Universal Tape™ 110 is used to seal any joints formed when a plurality of exterior gypsum boards 108 are placed together to form the wall. This embodiment does not utilize fiberglass batt insulation within this air space, but instead this air space is left empty to prevent the growth of mold.

Once the exterior gypsum board 108 is sealed with Universal Tape™ 110, it is coated with a vapor permeable, air and water barrier chemical composition to form a single layer 112. This prevents liquid water and humidity from passing into the building which is critical since water or humidity greater than 70% is required for mold growth. This chemical composition is preferably a liquid applied bituminous material polymer blend. It is more preferred that the chemical composition be a liquid applied asphalt polymer blend. It is still preferred that this asphalt polymer blend be more specifically elastomeric. The elastomeric property is important to accommodate building movement. The product must “move” with the building in order to prevent splitting which would permit water and/or humidity to enter the building.

The single layer 112 also provides superior thermal efficiency as recognized by the ASHRAE 90.1 This is due to the use of the liquid applied air/water barrier which greatly reduces air infiltration into the building and by the application of the continuous rigid foam plastic insulation to the exterior of the steel studs. Thermal efficiency has increased from 50% (for the traditional wall) to 80% (for the present invention). The product FW-100™ Frame Wall Air Barrier by Wall Guardian possesses these preferred characteristics. Another elastomer, Air-Bloc 31™ by Henry, can be substituted.

Once the single layer 112 is set, board insulation 114 is placed against the single layer 112. The board insulation 114 is preferably rigid foam plastic insulation board that is CFC free and recyclable. This board insulation 114 is more preferably extruded polystyrene, being approximately 2.0 inches thick. The purpose of this board insulation 114 is to move the dew point (condensation point) away from the steel studs 106. The product Dow CavityMate™ possesses these preferred characteristics.

Once the board insulation 114 is in place, exterior veneer 118 is placed adjacent to the board insulation 114. This exterior veneer 118 can be either brick or steel siding. A brick exterior veneer would be stacked horizontally and vertically to form a wall unit at a predetermined distance from the board insulation 114. The predetermined distance between the board insulation 114 and the brick exterior veneer forms an air space 116 between these two structures. This predetermined distance is preferably approximately one inch.

For steel siding, a starter strip (not shown) is generally provided. An initial row of steel siding panels (not shown) is then inserted into the starter strip and generally locked into place. Subsequent steel siding panels (not shown) are inserted row by row into the preceding row of steel siding panels ultimately to form a wall assembly.

FIG. 2 shows a perspective view of the second embodiment of the present invention. More particularly, the second embodiment shows a mold resistant stucco wall assembly 120. A foundation 102 is provided upon which the wall system 100 is assembled. Steel studs 106 are attached to the foundation 102 and once attached have a defined interior side 106 a and exterior side 106 b. A plurality of these steel studs 106 acts as a frame for the wall system 100. The wall system 120 is constructed around the steel studs 106. Beginning at the interior side 106 a of the steel studs 106 is interior finish gypsum board 104. This interior finish gypsum board 104 is attached to the steel studs 106. A product that resists the growth of mold, mildew and fungus is preferred such as Dens Armor Plus™ by Georgia-Pacific. On the exterior side 106 b of the steel studs 106 is placed exterior gypsum board 108.

The exterior gypsum board 108 is again preferably a glass mat gypsum substrate which is mold and moisture resistant. The glass mat gypsum substrate preferably contains a noncombustible water-resistant core, essentially gypsum, surfaced with a glass mat partially or completely embedded in the core. The water resistance of the glass mat gypsum substrate preferably has an average water absorption of not more than 10 weight percent after a two 11 hour immersion. For code compliance purposes, the exterior gypsum board 108 should comply with the current ASTM standard C 1177. The product Dens-Glass Gold™ by Georgia-Pacific possesses these preferred characteristics. The thickness of the steel studs 106 provides space between interior finish gypsum board 104 and exterior gypsum board 108 which can accommodate fiberglass insulation 122, preferably R-11 insulation. Universal Tape™ 110 is used to seal any joints formed when a plurality of exterior gypsum boards 108 are placed together to form the wall.

Once the exterior gypsum board 108 is sealed with universal tape 110, it is coated with a vapor permeable, air and water barrier chemical composition to form a single layer 112. This chemical composition is preferably a liquid applied bituminous material polymer blend. It is more preferred that the chemical composition be a liquid applied asphalt polymer blend. It is further preferred that this asphalt polymer blend be more specifically elastomeric. The product FW-100™ Frame Wall Air Barrier by Wall Guardian possesses these preferred characteristics.

Once the single layer 112 is set, foam insulation board 124 is placed against the single layer 112. The foam insulation board 124 is preferably polyisocyanurate, being approximately 1.0 inches thick. The product Quik R™ by Dow meets these requirements and can also function as a drainage plane and pressure relief system.

Once the foam insulation board 124 is in place, metal lath 126 is applied and attached through the foam insulation board 124 to the steel studs 106. Metal lath 126 is used as a platform to embed and attach the stucco to the wall assembly 120. Once the metal lath 126 is in place a stucco layer 128 can be applied.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention. 

1. A mold resistant exterior wall assembly for steel stud construction comprising: a plurality of steel studs situated in parallel along a foundation, once situated establishing an inside surface and an outside surface; a first wall member attached to the inside surface of said steel studs; a second wall member attached to the outside surface of said steel studs; an elastomeric component applied to said second wall member; a rigid insulation member applied to said elastomeric component; and exterior veneer applied a predetermined distance from said rigid insulation member.
 2. The mold resistant exterior wall assembly for steel stud construction of claim 1 wherein said second wall member is mold and moisture resistant.
 3. The mold resistant exterior wall assembly for steel stud construction of claim 2 wherein said second wall member comprises glass mat gypsum.
 4. The mold resistant exterior wall assembly for steel stud construction of claim 3 wherein said second wall member comprises a water-resistant gypsum core surfaced with a glass mat at least partially embedded in the gypsum core.
 5. The mold resistant exterior wall assembly for steel stud construction of claim 1 wherein said second wall member comprises a plurality of parallel wall member units.
 6. The mold resistant exterior wall assembly for steel stud construction of claim 5 further comprising a sealant to seal said plurality of parallel wall member units.
 7. The mold resistant exterior wall assembly for steel stud construction of claim 6 wherein said sealant is Universal Tape™.
 8. The mold resistant exterior wall assembly for steel stud construction of claim 1 wherein said elastomeric component is a liquid applied polymer.
 9. The mold resistant exterior wall assembly for steel stud construction of claim 8 wherein said elastomeric component is an asphalt polymer blend.
 10. The mold resistant exterior wall assembly for steel stud construction of claim 1 wherein said rigid insulation member is a rigid foam plastic insulation.
 11. The mold resistant exterior wall assembly for steel stud construction of claim 10 wherein said rigid insulation member comprises an extruded polystyrene.
 12. The mold resistant exterior wall assembly for steel stud construction of claim 10 wherein said rigid insulation member comprises a polyisocyanurate.
 13. The mold resistant exterior wall assembly for steel stud construction of claim 11 wherein said exterior veneer consists of brick and steel siding.
 14. The mold resistant exterior wall assembly for steel stud construction of claim 12 wherein said exterior veneer consists of stucco.
 15. The mold resistant exterior wall assembly for steel stud construction of claim 14 further comprising metal lath attached to said rigid insulation member.
 16. A method of exterior wall assembly for steel stud construction comprising the steps of: situating a plurality of steel studs in parallel along a foundation establishing an inside surface and outside surface; attaching a first wall member to the inside surface of said steel studs; attaching a second wall member to the outside surface of said steel studs; applying an elastomeric component to said second wall member; applying a rigid insulation member to said elastomeric component; and applying an exterior veneer a predetermined distance from said rigid insulation member.
 17. The method of exterior wall assembly for steel stud construction of claim 16 wherein said rigid insulation member comprises polystyrene.
 18. The method of exterior wall assembly for steel stud construction of claim 16 wherein said rigid insulation member comprises polyisocyanurate.
 19. The method of exterior wall assembly for steel stud construction of claim 17 wherein said exterior veneer consists of brick and steel siding.
 20. The method of exterior wall assembly for steel stud construction of claim 18 wherein said exterior veneer consists of stucco. 